Etching method

ABSTRACT

An etching method of etching a silicon nitride region with high selectivity is provided. In the etching method, a processing target object, having a silicon nitride region and a silicon-containing region having a composition different from the silicon nitride region, is accommodated in a processing vessel, and the silicon nitride region is selectively etched. In a first process, a deposit containing hydrofluorocarbon is formed on the silicon nitride region and the silicon-containing region by generating plasma of a processing gas containing a hydrofluorocarbon gas within the processing vessel. In a second process, the silicon nitride region is etched by radicals of the hydrofluorocarbon contained in the deposit. The first process and the second process are repeated alternately.

CROSS-REFERENCE TO RELATED APPLICATION

This Application is a U.S. national phase application under 35 U.S.C. §371 of PCT Application No. PCT/JP2017/017273 filed on May 2, 2017, whichclaims the benefit of Japanese Patent Application No. 2016-094659 filedon May 10, 2016, the entire disclosures of which are incorporated hereinby reference.

TECHNICAL FIELD

The various embodiments described herein pertain generally to an etchingmethod.

BACKGROUND ART

Conventionally, researches on an etching method for silicon nitride havebeen conducted. Patent Document 1 describes a method of etching anitride layer on a substrate anisotropically by using a gas containinghydrogen-rich hydrofluorocarbon, an oxidant and a carbon source.

Patent Document 2 discloses a method of etching silicon nitride at adeep position within a hole by using fluorine radicals originated fromfluorocarbon. Patent Document 3 recites a method of etching siliconnitride by using CH₂F₂, CH₃F or CHF₃.

Patent Document 1: Japanese Patent Laid-open Publication No. H11-260798

Patent Document 2: Japanese Patent Laid-open Publication No. 2002-319574

Patent Document 3: Japanese Patent Laid-open Publication No. H10-303187

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The conventional etching methods, however, have a drawback in thatetching selectivity for the silicon nitride is not sufficient.

In view of the foregoing, exemplary embodiments provide an etchingmethod capable of etching silicon nitride with high selectivity.

Means for Solving the Problems

In an exemplary embodiment, there is provided a first etching method ofselectively etching a silicon nitride region of a processing targetobject which is accommodated in a processing vessel and has the siliconnitride region and a silicon-containing region having a compositiondifferent from the silicon nitride region. The first etching methodincludes a first process of forming a deposit containinghydrofluorocarbon on the silicon nitride region and thesilicon-containing region by generating plasma of a processing gascontaining a hydrofluorocarbon gas within the processing vessel; and asecond process of etching the silicon nitride region by radicals of thehydrofluorocarbon contained in the deposit. The first process and thesecond process are repeated alternately.

As for the deposit which is originated from the hydrofluorocarbon andformed in the first process, an amount of the deposit on the siliconnitride region is smaller than an amount of the deposit on thesilicon-containing region having the different composition from thesilicon nitride region. In the second process, if the radicals areapplied to the deposit, the silicon nitride region is etched.Accordingly, as the first process and the second process are repeatedalternately, the silicon nitride region is etched with high selectivitywith respect to the silicon-containing region.

In a second etching method, the silicon-containing region contains atleast one silicon compound selected from the group consisting of SiC,SiOC, SiON, SiCN, SiOCN and SiO₂. These silicon-containing materialsaccompany a larger amount of the hydrofluorocarbon-originated deposit ascompared to the silicon nitride. Thus, the etching selectivity for thesilicon nitride can be sufficiently achieved.

In a third etching method, the hydrofluorocarbon gas contains at leastone gas selected from the group consisting of CH₃F, CH₂F₂, CHF₃. Thesehydrofluorocarbon gases have a smaller deposition amount on a surface ofthe silicon nitride region, as compared to other materials. Thus, thesilicon nitride region can be sufficiently etched.

In a fourth etching method, a ratio between a period of the firstprocess and a period of the second process is set such that an etchingamount of the silicon nitride region is at least five times as large asan etching amount of the silicon-containing region. In this case, sincethe silicon nitride can be etched with sufficiently high selectivity, adeep hole or a deep groove, which cannot be formed in the prior art, canbe easily formed.

In a fifth etching method, during the second process, the radicals ofthe hydrofluorocarbon contained in the deposit are generated by exposingthe deposit to plasma of a rare gas. If the deposit is exposed to theplasma of the rare gas, ions of rare gas atoms collide with the deposit,so that the radicals of the hydrofluorocarbon are generated from thedeposit. As a result, the silicon nitride region is etched depending ona surface state of the silicon nitride during the deposition and thegenerated radicals.

In a sixth etching method, the processing gas does not substantiallycontain oxygen. In this case, since surface oxidation does not takeplace as compared to a case where the processing gas contains oxygen, adifference in the deposition film caused by the difference in thematerials may be easily generated. Here, the expression of “does notsubstantially contain oxygen” implies that oxygen is not intentionallyintroduced into the processing gas and is assumed to refer to a casewhere an oxygen gas concentration in the processing gas is equal to orless than 2.0×10⁻¹⁰ mol/cm³ (this oxygen gas concentration is calculatedfor a case where air having a vacuum level of 0.025 T (3.3 Pa) andcontaining 20% of oxygen is decompressed).

Effect of the Invention

According to the etching methods of the exemplary embodiment asdescribed above, it is possible to etch the silicon nitride region withhigh selectivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A to FIG. 1C are diagrams illustrating an etching target objectaccording to an exemplary embodiment.

FIG. 2 is a diagram illustrating a plasma processing apparatus accordingto the exemplary embodiment.

FIG. 3 is a graph showing a relationship between a sputtering time (sec)and an etching amount (nm).

FIG. 4 is a graph showing a relationship between the sputtering time(sec) and the etching amount (nm).

FIG. 5 is a graph showing a relationship between the sputtering time(sec) and the etching amount (nm).

FIG. 6 is a graph showing a relationship between the sputtering time(sec) and the etching amount (nm).

FIG. 7 is a diagram illustrating a longitudinal cross sectionalstructure of a processing target object.

FIG. 8 is a diagram for describing a longitudinal cross sectionalstructure of the processing target object after an etching processing isbegun.

FIG. 9 is a graph for describing a variation of a deposition amount (nm)under various conditions.

FIG. 10 is a graph for describing a variation of a deposition thicknessratio (btm/top) under various conditions.

FIG. 11 is a graph for describing a variation of a deposition amount(nm) under various conditions.

FIG. 12 is a graph for describing a variation of a deposition thicknessratio (btm/top) under various conditions.

DETAILED DESCRIPTION

Hereinafter, various exemplary embodiments will be described withreference to accompanying drawings, which form a part of thedescription. In the various drawings, same or corresponding parts willbe assigned same reference numerals.

FIG. 1A to FIG. 1C are diagrams illustrating an etching target objectaccording to an exemplary embodiment.

FIG. 1A shows a state in which three layers are formed on a substrateSB. That is, a processing target object has a first region R1, a secondregion R2 and a third region R3 on the substrate SB, and these first tothird regions R1 to R3 are silicon-containing regions having differentcompositions. A material for the substrate SB is not particularlylimited. Here, in the present exemplary embodiment, the substrate SB ismade of, by way of example, Si. Further, in the present exemplaryembodiment, the first region R1 is a silicon nitride region (SiN_(x)) (xis an appropriate number); the second region R2, a SiCN region; and thethird region R3, a SiC region.

FIG. 1B is a diagram for describing a first process of an etchingprocessing and illustrates a state in which a deposit DP is deposited onthe first region R1, the second region R2 and the third region R3. Thedeposit DP is formed on surfaces of the respective regions as theseregions are exposed to plasma of a processing gas containing ahydrofluorocarbon gas (CH₃F, CH₂F₂, or CHF₃). Further, since FIG. 1A toFIG. 1C are diagrams for describing the deposit on the first to thirdregions, illustration of a deposit formed on the substrate SB when aplasma processing is performed on this structure is omitted. To form thedeposit DP, the processing target object is first accommodated in aprocessing vessel, and the plasma of the processing gas containing thehydrofluorocarbon gas is generated within the processing vessel so thatthe surfaces of the first region R1, the second region R2 and the thirdregion R3 are exposed to the corresponding plasma. In this depositionprocess, the deposit on the first region R1 made of the silicon nitridehas a smaller thickness as compared to the other two regions. Further, athickness of the deposit DP formed on the second region R2 made of theSiCN is smaller than a thickness of the deposit DP on the third regionR3 made of the SiC.

Subsequently, sputtering by a rare gas is performed.

FIG. 1C is a diagram for describing a second process of the etchingprocessing and illustrates a state in which a part of the deposit DP anda surface layer of the first region R1 are removed through thesputtering by the rare gas (desirably, the rare gas may be Ar, but He,Ne, Kr, Xe and Rn may also be used). In the second process, by exposingthe deposit DP to plasma of the rare gas, radicals of thehydrofluorocarbon contained in the deposit DP are generated. Toelaborate, if the deposit DP is exposed to the plasma of the rare gas,ions of rare gas atoms collide with the deposit DP, so that the radicalsof the hydrofluorocarbon are generated from the deposit DP. As a result,the first region R1 is etched depending on a surface state of the firstregion R1 (silicon nitride) during the deposition and the generatedradicals. Further, since the plasma of the rare gas sputters a surfaceof the deposit DP, a thickness of the deposit DP is decreased.

Thereafter, by repeating the first process and the second processalternately, the first region R1 is selectively etched.

As stated above, in the etching method according to the exemplaryembodiment, the processing target object having the silicon nitrideregion (the first region R1) and the silicon-containing regions (thesecond region R2 and the third region R3) having the compositionsdifferent from that of the silicon nitride region is accommodated in theprocessing vessel, and the first region R1 is selectively etched. Thisetching method includes the first process of forming the deposit DPcontaining the hydrofluorocarbon on the first region R1, the secondregion R2 and the third region R3 by generating the plasma of theprocessing gas containing the hydrofluorocarbon gas within theprocessing vessel; and the second process of etching the first region R1by the radicals of the hydrofluorocarbon contained in the deposit DP.The first process and the second process are alternately repeated.

As for the hydrofluorocarbon-originated deposit DP formed in the firstprocess, an amount of the corresponding deposit on the first region(silicon nitride region) is smaller than amounts of the deposit on thesilicon-containing regions having the different compositions from thefirst region. If the radicals are applied to the deposit DP in thesecond process, the first region R1 is etched. Accordingly, as the firstprocess and the second process are repeated alternately, the siliconnitride region is etched with high selectivity with respect to the othersilicon-containing regions.

Further, in the above-described etching method, the silicon-containingregion constituting the second region R2 or the third region R3 maycontain at least one silicon compound selected from the group consistingof SiC, SiOC, SiON, SiCN, SiOCN and SiO₂. As will be described later, ascompared to the silicon nitride, these silicon-containing materialsgenerate a larger amount of hydrofluorocarbon-originated deposit DP.Thus, the etching selectivity for the silicon nitride can besufficiently achieved.

Furthermore, the hydrofluorocarbon gas contains at least one gasselected from the group consisting of CH₃F, CH₂F₂, CHF₃. Thesehydrofluorocarbon gases have a smaller deposition amount on the surfaceof the silicon nitride region, as compared to other materials. Thus, thesilicon nitride region can be sufficiently etched.

In case that an internal pressure of the processing vessel is set to 30mT (4.0 Pa); 250 W is applied to an upper electrode of a plasmaprocessing apparatus; a DC voltage applied to the upper electrode is setto 0 V; a substrate temperature is set to 60° C.; and an Ar gas (1000sccm) and a hydrofluorocarbon gas (CH₃F (25 sccm)) are used as theprocessing gas, a ratio of the deposition amounts of the deposit DP onthe first region R1, the second region R2 and the third region R3 isfound to be 1:3:5. In case that CHF₃ is used as the hydrofluorocarbongas under the same conditions, a ratio between the deposition amount onthe first region R1 and the deposition amount on the third region R3becomes 1:4 at 60° C. Further, in case that the CHF₃ is used, the formeddeposit and a material directly thereunder are etched at differentetching rates by the Ar sputtering in the second process with a lapse ofsputtering time. In this case, SiO₂ is most readily etched, followed bySiN_(X) and SiC in this sequence.

Now, the plasma processing apparatus equipped with the processing vesselwill be explained.

FIG. 2 is a diagram illustrating the plasma processing apparatusaccording to the exemplary embodiment. A plasma processing apparatus 10shown in FIG. 2 is configured as a capacitively coupled plasma etchingapparatus and equipped with a substantially cylindrical processingvessel 12. An inner wall surface of the processing vessel 12 is made of,by way of example, anodically oxidized aluminum. This processing vessel12 is frame-grounded.

A substantially cylindrical supporting member 14 is provided on a bottomportion of the processing vessel 12. The supporting member 14 is madeof, by way of example, but not limitation, an insulating material.Within the processing vessel 12, the supporting member 14 is verticallyextended from the bottom portion of the processing vessel 12. Further, amounting table PD is provided within the processing vessel 12. Themounting table PD is supported by the supporting member 14.

The mounting table PD is configured to hold the wafer W on a top surfacethereof. The mounting table PD includes a lower electrode LE and anelectrostatic chuck ESC. The lower electrode LE is provided with a firstplate 18 a and a second plate 18 b. The first plate 18 a and the secondplate 18 b are made of a metal such as, but not limited to, aluminum andhave a substantially disk shape. The second plate 18 b is provided onthe first plate 18 a and electrically connected with the first plate 18a.

The electrostatic chuck ESC is provided on the second plate 18 b. Theelectrostatic chuck ESC includes a pair of insulating layers orinsulating sheets; and an electrode, which serves as a conductive film,embedded therebetween. The electrode of the electrostatic chuck ESC iselectrically connected to a DC power supply 22 via a switch 23. Theelectrostatic chuck ESC is configured to attract the wafer W by anelectrostatic force such as a Coulomb force generated by a DC voltageapplied from the DC power supply 22. Accordingly, the electrostaticchuck ESC is capable of holding the wafer W.

A focus ring FR is provided on a peripheral portion of the second plate18 b to surround an edge of the wafer W and the electrostatic chuck ESC.The focus ring FR is configured to improve etching uniformity. The focusring FR is made of a material which is appropriately selected dependingon a material of an etching target film. For example, the focus ring FRmay be made of quartz.

A coolant path 24 is provided within the second plate 18 b. The coolantpath 24 constitutes a temperature controller. A coolant is supplied intothe coolant path 24 from a chiller unit provided outside the processingvessel 12 via a pipeline 26 a. The coolant supplied into the coolantpath 24 is then returned back into the chiller unit via a pipeline 26 b.In this way, the coolant is supplied into the coolant path 24 to becirculated therein. A temperature of the wafer W held by theelectrostatic chuck ESC is controlled by adjusting a temperature of thecoolant.

Furthermore, the plasma processing apparatus 10 is provided with a gassupply line 28. Through the gas supply line 28, a heat transfer gas,e.g., a He gas, is supplied from a heat transfer gas supply device intoa gap between a top surface of the electrostatic chuck ESC and a rearsurface of the wafer W.

Further, the plasma processing apparatus 10 includes an upper electrode30. The upper electrode 30 is provided above the mounting table PD,facing the mounting table PD. The lower electrode LE and the upperelectrode 30 are arranged to be substantially parallel to each other.Formed between the upper electrode 30 and the lower electrode LE is aprocessing space S in which a plasma processing is performed on thewafer W.

The upper electrode 30 is supported at an upper portion of theprocessing vessel 12 with an insulating shield member 32 therebetween.In the exemplary embodiment, the upper electrode 30 is configured suchthat a distance from the top surface of the mounting table PD, i.e., amounting surface on which the wafer W is placed is variable in avertical direction. The upper electrode 30 may include an electrodeplate 34 and an electrode supporting body 36. The electrode plate 34faces the processing space S, and is provided with a multiple number ofgas discharge holes 34 a. In the exemplary embodiment, the electrodeplate 34 is made of silicon.

The electrode supporting body 36 is configured to support the electrodeplate 34 in a detachable manner, and is made of a conductive materialsuch as, but not limited to, aluminum. The electrode supporting body 36may have a water-cooling structure. A gas diffusion space 36 a is formedwithin the electrode supporting body 36. Multiple gas through holes 36 bare extended downwards from the gas diffusion space 36 a, and these gasthrough holes 36 b communicate with the gas discharge holes 34 a,respectively. Further, the electrode supporting body 36 is also providedwith a gas inlet opening 36 c through which a processing gas isintroduced into the gas diffusion space 36 a, and this gas inlet opening36 c is connected to a gas supply line 38.

The gas supply line 38 is connected to a gas source group 40 via a valvegroup 42 and a flow rate controller group 44. The gas source group 40includes a plurality of gas sources such as a source of thehydrofluorocarbon gas and a source of the rare gas. When necessary, thegas source group may further include a source of an oxygen (O₂) gas. Thehydrofluorocarbon gas is a gas containing at least one of, by way ofnon-limiting example, CH₃F, CH₂F₂ and CHF₃. Further, the rare gas is agas containing at least one of various rare gases such as an Ar gas anda He gas.

The valve group 42 includes a multiple number of valves, and the flowrate controller group 44 includes a multiple number of flow ratecontrollers such as mass flow controllers. Each of the gas sourcesbelonging to the gas source group 40 is connected to the gas supply line38 via each corresponding valve belonging to the valve group 42 and eachcorresponding flow rate controller belonging to the flow rate controllergroup 44.

Further, in the plasma processing apparatus 10, a deposition shield 46is provided along an inner wall of the processing vessel 12 in adetachable manner. The deposition shield 46 is also provided on an outerside surface of the supporting member 14. The deposition shield 46 isconfigured to suppress an etching byproduct (deposit) from adhering tothe processing vessel 12, and is formed by coating an aluminum memberwith ceramics such as Y₂O₃.

At the bottom side of the processing vessel 12, a gas exhaust plate 48is provided between the supporting member 14 and a side wall of theprocessing vessel 12. The gas exhaust plate 48 may be made of, by way ofexample, an aluminum member coated with ceramics such as Y₂O₃. Theprocessing vessel 12 is also provided with a gas exhaust opening 12 eunder the gas exhaust plate 48. The gas exhaust opening 12 e isconnected with a gas exhaust device 50 via a gas exhaust line 52. Thegas exhaust device 50 includes a vacuum pump such as a turbo molecularpump, and is capable of decompressing the space within the processingvessel 12 to a required vacuum level. Further, a carry-in/out opening 12g for the wafer W is provided at the side wall of the processing vessel12, and the carry-in/out opening 12 g is opened or closed by a gatevalve 54.

The plasma processing apparatus 10 further includes a first highfrequency power supply 62 and a second high frequency power supply 64.The first high frequency power supply 62 is configured to generate ahigh frequency power for plasma generation having a frequency rangingfrom 27 MHz to 100 MHz, for example, 40 MHz. The first high frequencypower supply 62 is connected to the lower electrode LE via a matchingdevice 66. The matching device 66 is a circuit configured to match anoutput impedance of the first high frequency power supply 62 and aninput impedance at a load side (lower electrode LE side).

The second high frequency power supply 64 is configured to generate asecond high frequency power for ion attraction into the wafer W, thatis, high frequency bias power having a frequency ranging from 400 kHz to40 MHz, for example, 13 MHz. The second high frequency power supply 64is connected to the lower electrode LE via a matching device 68. Thematching device 68 is a circuit configured to match an output impedanceof the second high frequency power supply 64 and the input impedance atthe load side (lower electrode LE side).

Further, the plasma processing apparatus 10 is further equipped with aDC power supply 70. The DC power supply 70 is connected to the upperelectrode 30. The DC power supply 70 is configured to generate anegative DC voltage and apply this DC voltage to the upper electrode 30.If the negative DC voltage is applied to the upper electrode 30,positive ions existing in a processing space S collide with theelectrode plate 34. Accordingly, secondary electrons and/or silicon maybe released from the electrode plate 34.

Further, in the exemplary embodiment, the plasma processing apparatus 10may further include a control unit Cnt. The control unit Cnt isimplemented by a computer including a processor, a storage unit, aninput device, a display device, and so forth, and is configured tocontrol individual components of the plasma processing apparatus 10. Inthe control unit Cnt, an operator can input commands through the inputdevice to manage the plasma processing apparatus 10, and an operationalstatus of the plasma processing apparatus 10 can be visually displayedon the display device. Further, the storage unit of the control unit Cntstores therein a control program for controlling various processingsperformed in the plasma processing apparatus 10 by the processor, or aprogram for allowing each component of the plasma processing apparatus10 to perform a processing according to processing conditions, i.e., aprocessing recipe.

In the aforementioned first process, a Si wafer W is used as an exampleof the substrate, and the aforementioned hydrofluorocarbon gas issupplied into the processing vessel 12 from the gas source group 40 viathe flow rate controller group 44, the valve group 42 and the gas supplyline 38. Further, the high frequency power from the first high frequencypower supply 62 is supplied to the lower electrode LE, and the highfrequency bias power from the second high frequency power supply 64 issupplied to the lower electrode LE.

Further, in the first process, a pressure of the space within theprocessing vessel 12 is set to a preset pressure by the gas exhaustdevice 50. By way of example, the pressure of the space within theprocessing vessel 12 is set to a pressure within a range from 20 mTorr(2.666 Pa) to 50 mTorr (6.666 Pa). In addition, in the first process, adistance between the upper electrode 30 and the top surface of themounting table PD is set to be in a range from 20 mm to 50 mm.Accordingly, plasma of the processing gas is generated within theprocessing vessel 12, and the wafer W placed on the mounting table PD isexposed to this plasma. Moreover, in the first process, the negative DCvoltage may be applied to the upper electrode 30 from the DC powersupply 70. When the first process is performed, operations of theindividual components of the plasma processing apparatus 10 may becontrolled by the control unit Cnt.

In the first process, initially, active species of atoms and/ormolecules originated from the hydrofluorocarbon, for example, activespecies of fluorine and/or hydrofluorocarbon collide with the first tothird regions R1 to R3. Accordingly, in the first process, the depositDP is formed on the first region R1. The film thickness of the depositDP increases with a lapse of a processing time of the first process. Inthis first process, a surface state of the first region R1 is slightlymodified.

Further, the processing gas used in the first process does notsubstantially contain oxygen. In this case, since surface oxidation doesnot take place as compared to a case where the processing gas containsoxygen, a difference in the deposition film caused by the difference inthe materials may be easily generated. Here, the expression of “does notsubstantially contain oxygen” implies that oxygen is not intentionallyintroduced into the processing gas and is assumed to refer to a casewhere an oxygen gas concentration in the processing gas is equal to orless than 2.0×10⁻¹⁰ mol/cm³ (this oxygen gas concentration is calculatedfor a case where air having a vacuum level of 0.025 T (3.3 Pa) andcontaining 20% of oxygen is decompressed).

In the second process, the Ar is used as the rare gas, and sputtering ofthe deposit DP is performed by generating plasma of the Ar gas. Thefirst region R1 is etched by the radicals of the hydrofluorocarboncontained in the deposit DP. In the second process, the wafer W afterbeing subjected to the first process is exposed to the plasma of therare gas. A processing time of the second process and the processingtime of the first process may be set as required. In the exemplaryembodiment, a ratio of the processing time of the first process withrespect to a sum of the processing times of the first and secondprocesses may be set to be in the range from 5% to 30%.

In case of performing the second process by using the plasma processingapparatus 10, the rare gas is supplied from the gas source group 40.Further, in the second process, if the deposit remains on the SiN_(X),an oxygen gas (O₂ gas) may also be applied along with the rare gas.Furthermore, in the second process, the high frequency power from thefirst high frequency power supply 62 is supplied to the lower electrodeLE. Further, in the second process, the high frequency bias power fromthe second high frequency power supply 64 may also be supplied to thelower electrode LE. By way of example, the pressure of the space withinthe processing vessel 12 may be set to be in the range from 20 mTorr(2.666 Pa) to 50 mTorr (6.666 Pa). Moreover, in the second process, thedistance between the upper electrode 30 and the top surface of themounting table PD is set to be in the range from 20 mm to 50 mm.Accordingly, the plasma of the rare gas is generated within theprocessing vessel 12, and the wafer W placed on the mounting table PD isexposed to this plasma. Further, in the second process, the negative DCvoltage may be applied to the upper electrode 30 from the DC powersupply 70. In addition, while the second process is performed, theoperations of the individual components of the plasma processingapparatus 10 may be controlled by the control unit Cnt.

In the second process, active species of the rare gas, for example, ionsof atoms of the rare gas collide with the deposit DP. The etching of thefirst region R1 is performed by the hydrofluorocarbon radicals in thedeposit DP. Further, through the second process, the film thickness ofthe deposit DP on the first region R1 is decreased. In addition, in thesecond process, film thicknesses of the deposit DP on the second regionR2 and the third region R3 are also decreased.

In the above-stated etching method, the first process is performed againafter the second process is completed. The film thickness of the depositDP is reduced through the previous second process. Thus, if the wafer Wis exposed to the plasma of the aforementioned processing gas byperforming the first process again, the first region R1 can be furtheretched. Thereafter, by performing the second process again, the firstregion R1 can be etched by the hydrofluorocarbon radicals in the depositDP.

In the above-described etching method, it is determined whether a stopcondition is satisfied. The stop condition is satisfied when arepetition number of a cycle including the first process and the secondprocess reaches a preset number of times. If the stop condition is notsatisfied, the cycle including the first process and the second processis performed again. If the stop condition is met, on the other hand, theetching is ended.

In the above-stated etching method, by alternately repeating the firstprocess and the second process multiple times, the first region R1 canbe continually etched. Further, in the above-described etching method,the first region R1 can be etched selectively with respect to the secondregion R2 and the third region R3.

Moreover, in the above-described etching method, only an etching amountEA1 of the first region R1 (silicon nitride region) is increased,whereas an etching amount EA2 of the second region R2 and the thirdregion R3 (silicon-containing regions) becomes substantially zero. Aratio (R=T2/T1) between a period T1 (sec) of the first process and aperiod T2 (sec) of the second process may be set to be 3≤R≤20.

In this case, since the silicon nitride can be etched with sufficientlyhigh selectivity, a deep hole or a deep groove, which cannot be formedin the prior art, can be easily formed.

FIG. 3 is a graph showing a relationship between the sputtering time(the period T2 of the second process) (sec) and the etching amounts (nm)of individual regions.

As basic conditions, in the first process, a substrate temperature TEMPis set to 0° C.; an internal pressure of the processing vessel is set to30 mT; high frequency powers of 100 W and 0 W are applied to the upperelectrode and the lower electrode, respectively; and CH₃F and Ar aremixed at a ratio of 50:1000 as the processing gas. Further, in thesecond process, the substrate temperature TEMP is set to 0° C.; theinternal pressure of the processing vessel is set to 30 mT; highfrequency powers of 100 W and 50 W are applied to the upper electrodeand the lower electrode, respectively; and CH₃F and Ar are mixed at aratio of 0:1000 as the processing gas. The tendency shown on this graphis also observed in experiments where the substrate temperature is setto be in the range from 0° C. to 60° C.

Experiments are performed by setting the first period T1 to be 5 sec andthe second period T2 to be 5 sec, 15 sec, 30 sec, 45 sec and 60 sec. Ifthe second period T2, which is the sputtering time, becomes equal to orlarger than 30 sec, the etching amount of the first region (siliconnitride) is dramatically increased as compared to other materials (SiON,SiCN, SiOC, SiC, SiO₂). Further, if it is assumed that SiOCN has a statebetween SiON and SiCN, the etching amount of the SiOCN is alsodramatically increased.

If R (=T2/T1) is equal to or larger than 6 and equal to or less than 12at the substrate temperature of 0° C., the etching amount of the firstregion (silicon nitride) can be increased as compared to those of theother materials.

FIG. 4 is a graph showing a relationship between the sputtering time(the period T2 (sec) of the second process) and the etching amounts (nm)of the respective regions.

This graph is obtained under the conditions where the substratetemperature is changed to 20° C. from the aforementioned basicconditions.

The experiments are performed by setting the first period T1 to be 5 secand the second period T2 to be 5 sec, 15 sec, 30 sec, 45 sec and 60 sec.If the second period T2, which is the sputtering time, becomes equal toor larger than 30 sec, the etching amount of the first region (siliconnitride) is dramatically increased as compared to those of othermaterials (SiON, SiCN, SiOC, SiC, SiO₂).

If R (=T2/T1) is equal to or larger than 6 and equal to or less than 9at the substrate temperature of 20° C., the etching amount of the firstregion (silicon nitride) can be increased as compared to those of theother materials. Meanwhile, if R (=T2/T1) is equal to or larger than 9,the etching amount of the first region can be set to be 5 times as largeas those of SiON and SiO₂.

FIG. 5 is a graph showing a relationship between the sputtering time(the period T2 (sec) of the second process) and the etching amounts (nm)of the respective regions.

This graph is obtained under the conditions where the substratetemperature is changed to 60° C. from the aforementioned basicconditions.

The experiments are performed by setting the first period T1 to be 5 secand the second period T2 to be 5 sec, 15 sec, 20 sec, 25 sec, 30 sec, 45sec, 60 sec, 75 sec and 90 sec. If the second period T2, which is thesputtering time, becomes equal to or larger than 30 sec, the etchingamount of the first region (silicon nitride) is dramatically increasedas compared to those of other materials (SiON, SiCN, SiOC, SiC, SiO₂).

If R (=T2/T1) is equal to or larger than 5 and equal to or less than 6at the substrate temperature of 60° C., the etching amount of the firstregion (silicon nitride) can be increased as compared to those of theother materials.

FIG. 6 is a graph showing a relationship between the sputtering time(the period T2 (sec) of the second process) and the etching amounts (nm)of the respective regions.

This graph is obtained under the conditions where the substratetemperature is changed to 100° C. from the aforementioned basicconditions.

The experiments are performed by setting the first period T1 to be 5 secand the second period T2 to be 5 sec, 15 sec, 30 sec, 45 sec and 60 sec.If the second period T2, which is the sputtering time, becomes equal toor larger than 30 sec, the etching amount of the first region (siliconnitride) is increased as compared to those of the other materials (SiON,SiCN, SiOC, SiC, SiO₂).

If R (=T2/T1) is equal to or larger than 6 at the substrate temperatureof 100° C., the etching amount of the first region (silicon nitride) canbe increased as compared to those of the other materials.

As stated above, in the first and second processes, the etchingselectivity is improved when the temperature TEMP of the substrate asthe processing target object is in the range from 0° C. to 100° C.Particularly, this effect becomes conspicuous at the substratetemperature ranging from 0° C. to 60° C., and more conspicuous at thesubstrate temperature ranging from 0° C. to 20° C.

FIG. 7 is a diagram illustrating a longitudinal sectional structure of aprocessing target object.

A first region R1 is provided on a substrate SB, and a second region R2is provided at both sides of the first region R1. These regions may havea fin structure, and a longitudinally elongated structure is used as anyof various electronic circuit devices such as a transistor and acapacitor. The aforementioned etching is performed on this structure.

FIG. 8 is a diagram illustrating a longitudinal sectional structure ofthe processing target object after the etching processing is begun.

In this etching, a deep recess is formed at a central portion, and abottom surface of the recess becomes a surface of the first region R1,and the second region R2 remains at both sides of the first region R1. Adeposit DP is formed on a side surface and a bottom surface of therecess, and, also, on an end surface of an opening of the recess.

A maximum value of the thickness of the deposit DP on a top surface ofthe second region R2 is referred to as t_(s); a maximum value of aprotrusion amount of the deposit DP protruded inwardly from the sidesurface of the recess, t₁; a maximum value of the thickness of thedeposit DP formed on the surface of the first region R1 located at abottom portion of the recess, t_(b).

FIG. 9 is a graph for describing a variation of a deposition amount (mm)under various conditions.

As basic conditions, in the first process, the substrate temperatureTEMP is set to 60° C.; CH₃F is used as the processing gas; the internalpressure (press) of the processing vessel is set to 30 mT; the highfrequency power HF of 500 W is applied to the upper electrode; the highfrequency power of 0 W is applied to the lower electrode; and the DCvoltage DCS of the DC power supply 70 is set to 0 V; CH₃F and Ar aremixed at a ratio of 50:1000. If the various parameters are varied, it isfound out that the deposition amount tends to increase as the powerlevel of the high frequency power HF increases.

FIG. 10 is a graph showing a thickness ratio (btm/top) of the depositunder the conditions of FIG. 9. In the above-stated deposition process,the thickness ratio (btm/top) may fall within the range from 0.25 to0.75 even if the conditions are changed.

FIG. 11 is a graph for describing a variation of the deposition amount(nm) under various conditions.

As basic conditions, in the first process, the substrate temperatureTEMP is set to 60° C.; CH₃F is used as the processing gas; the internalpressure (press) of the processing vessel is set to 30 mT; the highfrequency power HF of 500 W is applied to the upper electrode; the highfrequency power of 0 W is applied to the lower electrode; and the DCvoltage DCS of the DC power supply 70 is set to 0 V; CH₃F and Ar aremixed at a ratio of 50:1000. While varying the various parameters, it isfound out that the deposition amount tends to increase as the powerlevel of the high frequency power HF increases.

FIG. 12 is a graph showing the thickness ratio (btm/top) of the depositunder the conditions of FIG. 11. In the above-stated deposition process,the thickness ratio (btm/top) may fall within the range from 0.45 to1.75 even if the conditions are changed.

Furthermore, in the above-described etching method, the processing gasused in the first process does not contain oxygen. If CH₃F, Ar and O₂are simply mixed at a ratio of 30:50:0˜60 (sccm) and the silicon nitrideis etched at a temperature of 60° C. for 60 seconds, the selectiveetching rate of the silicon nitride is 12.6 times as high as that of SiCat maximum (O₂ flow rate: 15 sccm), and the selective etching rate ofthe silicon nitride is 7.5 times as high as that of SiOC at maximum (O₂flow rate: 15 sccm). When the aforementioned first and second processesare performed, these etching ratios become infinite at maximum. As canbe seen from these experiments, highly selective etching is enabled.

So far, the various exemplary embodiments have been described. However,the above-described exemplary embodiments are not limiting and variouschanges and modifications may be made. By way of example, in the abovedescription, the capacitively coupled plasma processing apparatus 10 isdescribed as an example of the plasma processing apparatus used toimplement the above-stated etching method. However, any of various kindsof plasma processing apparatus using various kinds of plasma sources maybe used. By way of non-limiting example, various kinds of plasmaprocessing apparatuses such as an inductively coupled plasma processingapparatus and a plasma processing apparatus using a surface wave such asa microwave as a plasma source may be used.

EXPLANATION OF CODES

-   10: Plasma processing apparatus-   12: Processing vessel-   PD: Mounting table-   ESC: Electrostatic chuck-   LE: Lower electrode-   30: Upper electrode-   40: Gas source group-   50: Gas exhaust device-   62: First high frequency power supply-   64: Second high frequency power supply-   70: DC power supply-   W: Wafer-   DP: Deposit-   R1: First region-   R2: Second region

We claim:
 1. An etching method, comprising: accommodating, within aprocessing vessel, a processing target object having a silicon nitrideregion and a silicon-containing region, wherein the silicon-containingregion has a composition different from the silicon nitride region, andthe silicon nitride region and the silicon-containing region areexposed; a first process of forming a deposit containinghydrofluorocarbon on the silicon nitride region and thesilicon-containing region by generating plasma from a processing gascontaining a hydrofluorocarbon gas within the processing vessel; and asecond process of sputtering the deposit by active species of atoms of arare gas in plasma generated from the rare gas and etching the siliconnitride region by radicals generated from the hydrofluorocarboncontained in the deposit, wherein the first process and the secondprocess are repeated alternately.
 2. The etching method of claim 1,wherein the silicon-containing region contains at least one siliconcompound selected from the group consisting of SiC, SiOC, SiON, SiCN,SiOCN and SiO₂.
 3. The etching method of claim 1, wherein thehydrofluorocarbon gas contains at least one gas selected from the groupconsisting of CH₃F, CH₂F₂ and CHF₃.
 4. The etching method of claim 1,wherein a ratio between a period of the first process and a period ofthe second process is set such that an etching amount of the siliconnitride region is at least five times as large as an etching amount ofthe silicon-containing region.
 5. The etching method of claim 1,wherein, in the second process, the radicals generated from thehydrofluorocarbon contained in the deposit are generated by exposing thedeposit to the plasma of the rare gas.
 6. The etching method of claim 1,wherein an oxygen gas concentration in the processing gas is equal to orless than 2.0×10⁻¹⁰ mol/cm³.
 7. The etching method of claim 1, whereinthe second process includes generating the plasma from the rare gas andexposing a surface of the processing target object to the generatedplasma.
 8. The etching method of claim 1, wherein, in the first processand the second process, a temperature of the processing target object isset to be in the range from 0° C. to 100° C.
 9. The etching method ofclaim 1, wherein the first process and the second process are performedin the same processing vessel without carrying-out the processing targetobject.
 10. The etching method of claim 1, wherein, in the firstprocess, a surface of the silicon nitride region is modified.
 11. Theetching method of claim 1, wherein the silicon nitride region and thesilicon-containing region are exposed.
 12. The etching method of claim1, wherein the silicon-containing region comprises a SiCN regioncontaining SiCN and a SiC region containing SiC.
 13. The etching methodof claim 1, wherein the silicon-containing region contains at least onesilicon compound selected from the group consisting of SiC, SiOC, SiON,SiCN, SiOCN and SiO₂, and wherein the hydrofluorocarbon gas contains atleast one gas selected from the group consisting of CH₃F, CH₂F₂ andCHF₃.
 14. The etching method of claim 1, wherein a ratio of a processingtime of the first process with respect to a sum of processing times ofthe first and second processes is set to be in a range from 5% to 30%.15. The etching method of claim 1, wherein the processing vesselincludes a lower electrode on which the processing target object isplaced and an upper electrode facing the lower electrode, and wherein,in the first process, a pressure of a space within the processing vesselis set to a pressure within a range from 20 mTorr to 50 mTorr, and adistance between the upper electrode and a top surface of a mountingtable including the lower electrode is set to be in a range from 20 mmto 50 mm.
 16. The etching method of claim 1, wherein the processingvessel includes a lower electrode on which the processing target objectis placed and an upper electrode facing the lower electrode, andwherein, in the first process, a negative voltage is applied to theupper electrode.
 17. The etching method of claim 1, wherein theprocessing vessel includes a lower electrode on which the processingtarget object is placed and an upper electrode facing the lowerelectrode, and wherein, in the second process, a pressure of a spacewithin the processing vessel is set to a pressure within a range from 20mTorr to 50 mTorr, and a distance between the upper electrode and a topsurface of a mounting table including the lower electrode is set to bein a range from 20 mm to 50 mm.
 18. The etching method of claim 1,wherein the processing vessel includes a lower electrode on which theprocessing target object is placed and an upper electrode facing thelower electrode, and wherein, in the second process, a negative voltageis applied to the upper electrode.
 19. An etching method, comprising:accommodating, within a processing vessel, a processing target objecthaving a silicon nitride region and a silicon-containing region, whereinthe silicon-containing region has a composition different from thesilicon nitride region, and the silicon nitride region and thesilicon-containing region are exposed; a first process of forming adeposit containing hydrofluorocarbon on the silicon nitride region andthe silicon-containing region by generating plasma from a processing gascontaining a hydrofluorocarbon gas within the processing vessel; and asecond process of sputtering the deposit by active species of atoms of arare gas in plasma generated from the rare gas and etching the siliconnitride region by radicals generated from the hydrofluorocarboncontained in the deposit, wherein, in the first process, a thickness ofthe deposit formed on the silicon-containing region is thicker than athickness of the deposit formed on the silicon nitride region, and inthe second process, the deposit on the silicon-containing regionsuppresses the silicon-containing region from being substantiallyetched, and a ratio of a processing time of the first process withrespect to a sum of processing times of the first and second processesis set to be in a range from 5% to 30%.
 20. The etching method of claim19, wherein the silicon-containing region comprises a SiCN regioncontaining SiCN and a SiC region containing SiC.